Fuel oil is a fraction of oil obtained from oil refining process, either as a distillate or a residue and is often used as fuel for power stations, marine engines and similar. The aim of a catalytic cracker in refinery processing is to increase the quantity of lighter constituents or gasoline from the crude processed. While the intention is to retain the catalyst particles or fines, often simply called “cat fines”, in the catalytic cracker due to the high cost of the replacement of the material, this is not entirely possible to do so.
In particular the heavier part of the fuel oil, which is also referred to as “HFO”, often comprises considerable amounts of catalytic fines. The catalytic fines are hard, abrasive crystalline particles of alumina, silica, and/or alumina silica that can be carried over from the fluidic catalytic cracking process of residual fuel stocks. Particle size can range from sub-micron to greater than sixty microns in size. These particles become more common the higher the viscosity of the oil. HFO is often used as motor fuel e.g. in the marine industry, for example as fuel in vessels in which situation the HFO is called bunker fuel, which is the heaviest part of the oil. Also certain lighter oil types can comprise catalytic fines e.g. Marine Diesel Oil (MDO), which is a middle distillate fuel oil which can contain certain amounts, such as 5-10% by volume of residual fuel oil from transportation contamination and/or heavy fuel oil blending. The catalytic fines often accumulate in the fuel tanks which may give rise to very high concentrations of catalytic fines.
The hard abrasive catalytic fines can cause increased and at times severe wear in the engine as well as in fuel pumps, delivery valves, fuel injectors, piston rings, piston rods and other parts in contact with the HFO.
It is not only the amount of the catalytic fines that is important; the nominal size of the particles may also be relevant. The size of the particles can vary from very small (less than a micron) to larger than 60 microns. The main part of the catalytic fines is expected to be relatively spherical, however, it has also been observed that some parts of the catalytic fines can be elongated and with a small cross sectional area in one direction such catalytic fines can pass through even the finest filters and cause damage to the engine.
ISO 8217:2010 recommendation (http://www.dnv.com/industry/maritime/servicessolutions/fueltesting/fuelqualitytesti ng/iso8217fuelstandard.asp) specifies that the content of catalytic fines in the fuel oil delivered on board may not exceed a maximum of 60 ppm (w/w). Marine engine manufactures typically recommend that HFO oils that are consumed shall have less than 15 ppm of catalytic fines.
Therefore several cleaning or extraction systems for reducing the amount of catalytic fines in the fuel oil have been provided e.g. on board the vessels.
Centrifuges in combination with a settling tank are generally accepted within the marine industry as the fuel cleaning system of choice. Filters are mainly considered as a safety to pick up larger particles so that these particles do not reach the engine, and do not as such “clean” the fuel. Other extracting/cleaning systems include the separators described in US 2009/0120836 as well as the separators marketed by Alfa Laval under the name S-separator and P-separator for marine use.
Even though large efforts are made to remove catalytic fines it is practically impossible to remove all catalytic fines.
If properly operated, an extracting device has the capability to remove catalytic fines that are larger than 10 microns. However, the majority of catalytic fines smaller than five microns will not be removed due to small size and their relative light weight.
Furthermore it is very difficult to determine the amount of catalytic fines in fuel oil. Today the only way to obtain a reasonable determination of the amount of catalytic fines in a fuel, is to send a test sample to a dedicated laboratory. The test performed is based on general chemistry analytic methods and is generally a very time consuming and expensive test and only a few laboratories offer such tests.
The object of the invention is to provide a new and reliable method for determining catalytic fines in fuel oil. In particular the object of the invention is to provide a method for determining catalytic fines in fuel oil where the determination can be performed on the location in a relative simple way.